1. Field of the Invention
The invention relates to alkanolamine salts of cyclic amide acids as metal corrosion inhibitors in aqueous systems.
2. Description of the Prior Art
Technical processes which take place in the presence of water always involve the problem of corrosion protection if corrosion endangered metals such as iron, aluminum, zinc, copper or their alloys are involved in these processes such as cleaning processes, the use of cooling water or cooling lubricants as well as hydraulic fluids. With such process media the additional problem of pronounced foaming is incurred particularly in those cases where substances with surfactant properties are present as corrosion inhibitors. To date this problem could only be solved by added foam inhibitors which when they did not disturb the mentioned processes rendered them less economical.
German published application No. 2,758,123 describes alkanolamine salts of maleic-N-(C.sub.8 - to C.sub.12)-alkyl amide acids by means of which these problems can be solved if the salts are present in the process medium in low concentrations. U.S. Pat. No. 2,378,442 describes calcium salts of N-alkylated phthalamide acids as rust inhibiting lubricating oil additives, and U.S. Pat. No. 3,095,286 describes cyclic amide acids as corrosion inhibitors. However, in accordance with the above-mentioned literature references, these compounds are oil- but not water-soluble, and they are used only as additives in lubricating oil or fuels.
Certain applications, for instance, when contact corrosion between various metals is to be prevented such as in metal cutting, require higher concentrations of inhibitors in order to provide sufficient corrosion protection. For metal cutting such as drilling, threading, milling, sawing or grinding of material pieces, the low foaming property of the process medium is of particular importance. For such higher concentrations, the maleic amide acid salts disclosed in the above-mentioned literature reference are not effective in control of foam.
The goal of this invention is to provide substances which do not foam even in higher concentrations while otherwise providing at least equal corrosion protection as compared to prior art corrosion inhibitors. Surprisingly, the goal of the invention was reached with alkanolamine salts of cyclic amide acids as further described below.